A coil spring manufactured by performing an additional process at an end (e.g., a coil spring having a pigtail formed on an end) is known. In order to manufacture this type of coil spring, first, a cylindrical coil spring (semi-finished product) is formed by winding a wire, which is the material of the coil spring, on a coiling mandrel, and an additional process is performed at an end of the cylindrical coil spring so as to be formed into the final form. In Japanese Patent Application Publication No. 2005-349447, a forming device for forming a pigtail at an end of a cylindrical coil spring is disclosed. In this forming device, a forming jig is attached to a rotating shaft. In addition, one end (open end) of the wire of the cylindrical coil spring is fixed to the forming jig (coiling mandrel) by a first locking mechanism, and, within the wire of the coil spring, the location that starts the formation of the pigtail is clamped by a second locking mechanism. Then, by rotating the rotating shaft about its axis and moving the rotating shaft within a plane orthogonal to the rotational axis, the wire of the coil spring is wound on the forming jig to form the pigtail at an end of the cylindrical coil spring.